One issue that arises is modern computing systems is that many different types of memory modules can be used. Each different type of memory module may have different random access memory (RAM) parameters that have to be accounted for. As a consequence, it is desirable for a host system to have the capability to detect the presence of memory modules. The Serial Presence Detect (SPD) standard was developed by the Joint Electron Device Engineering Council (JEDEC) and is described in JEDEC Standard No. 21-C. The SPD standard implements presence detection serially using an address map specified by the SPD standard.
A memory module compliant with the SPD standard holds the SPD data in a non-volatile memory, such as an 8-pin serial Read Only Memory (ROM) or Electronically Erasable Programmable Read Only Memory (EEPROM). During a startup of a computer, the BIOS of the host system serially reads the SPD memory parameters from the non-volatile memory and configures the system based on the SPD memory parameters. SPD data is arranged as table entries corresponding to positions on a look-up table specified by the JEDEC standard. A particular presence detect (PD) aspect may, for example, be represented by one or more bytes.
FIG. 1 illustrates an SPD content table described by JEDEC standard No. 21-C. JEDEC standard No. 21-C specifies SPD data types that include lookup table entries, binary data, optional data, and checksums. The lookup table entries include tRAC, tCAC, # of banks, number of row addresses, number of column addresses, error detection/correction, refresh rates, data width and interface standards.
One drawback with conventional SPD is that it is intended to statically fix the memory parameters to one set of parameters certain to work. In contrast, in many types of computing systems it is desirable to have the freedom to adjust memory timing parameters based on different considerations, needs, or preferences.
What is desired is an apparatus, system, and method to extend the capabilities of SPD for more complex memory applications.